Electrical heating element



Nov. 14, 1950 A. P. CHALLENNER ELECTRICAL HEATING ELEMENT 2 Sheets-Sheet1 Filed June 22, 1950 grwvm/fm finse/ Cha//enn Nov. 14, 1950 A- P.CHALLENNER 2,529,914

ELECTRICAL HEATING ELEMENT Filed June 22, 1950 2 Sheets-Sheet 2 Ansel I?Ch al/enner Patented Nov. 14, 1950 ELECTRICAL HEATING ELEMENT Ansel P.Challenner, Norman, Oklm, minor to Denison Mattress Factory, Denison,Tex a partnership Application June 22, 1950, Serial No. 169,623

6 Claims.

relatively small size so that the elements may be 1 flexed or bent to aconsiderable degree without damage, and also whereby electricalconnections need be made to one end only of said element.

A particular object of the invention is to provide an improved heatingelement including a pair of concentric conductors adapted to beconnected to opposite poles or terminals of an electrical circuit, saidconductors being enclosed in an insulating shield whereby any shortcircuits or breaks which may occur in the circuit will result in an arewithin said insulating shield rather than exposing surrounding materialto the influence and danger of such an arc.

Another object of the invention is to provide an improved heatingelement of the character described wherein the concentric conductors areseparated by an insulating material, said insulating materialfunctioning to insulate the conductors one from another, to conduct heatoutwardly from the central conductor, and to generate a certain degreeof heat by reason of its dielectric loss.

Yet another object of the invention is to provide an improved heatingelement having a central conductor surrounded by an outer tubularconductor spaced therefrom by insulating material, the compositeconductors being surrounded by an insulating shield whereby thepossibility of electrical shock is minimized since the differences ofelectrical potential are confined to the interior of the compositeconductor.

An important object of the invention is to provide an improvedelectrical heating element employing electric power of high frequency incoaxial conductors whereby heating may be effected through dielectricloss within the element.

A particular object of the invention is to pro- -vide an improvedelectrical heating element permitting the passing of a high frequencyalternating electrical current through a pair of concentric conductorsseparated by an insulating material having a high dielectric losswhereby heat is generated by the leakage of electrical current throughthe insulating material.

An important object the invention is to provide an improved electricalheating element having a pair of concentric conductors connected at oneend to a suitable source of power supply and having their opposite endsshorted together wherein the voltage drop in the outer conductor isrelatively small so that a greater degree of safety is insured.

A construction designed to carry out the invention will be hereinafterdescribed together with other features of the invention.

The invention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawings,wherein examples of the invention are shown, and wherein:

Fig. l is a view in elevation of a portion of a heating elementconstructed in accordance with this invention with various of the layersand conductors being broken away to illustrate the structure thereof.

Fig. 2 is a view similar to Figure 1 and illustrating a modified form ofthe invention.

Fig. 3 is a view similar to Fig. 1 and illustrating a still furthermodification of the invention,

Fig. 4 is a cross-sectional view taken on the line 4-4 of Fig. 1,

Fig. 5 is a cross-sectional view taken on the line 5-5 of Fig. 2,

Fig. 6 is a cross-sectional view taken on the line G6 of Fig. 3,

Fig. '7 is a schematic view of the heating element arranged in a blanketand coupled to a high frequency source of energy,

Fig. 8 is an enlarged schematic view of the coupling arrangement,

Fig. 9 is an enlarged view of the remote end of the heating element, and

Fig. 10 is a schematic view of the heating element arranged in a blanketand connected to a low frequency source of energy.

This application is a continuation-in-part of my copending application,Serial No. 61,488, filed November 22, 1948, which, in turn, was acontinuation-in-part of my application, Serial No. 787,781, filedNovember 24, 1947, both abandoned.

In the drawings in Fig. l, the numeral ll designates a centralelectrical conductor or wire which may be formed of copper or any othersimilar, low-resistance conducting material or metallic alloy. Thedrawing is greatly magnified to illustrate clearly the structure of theheating element contemplated by this invention. In actual practice, theconductor 10 would be of the magnitude of several thousandths of an inchin diameter, such slenderness of the conductor permitting it to bendupon a very small radius and allowing it to undergo repeated flexing andbending without undue hardening or fracture.

The conductor III is covered with a covering or casing ll of insulatingmaterial. The casing ii may be composed of glass fibers woven or formedinto suitable strands or cords and arranged around the conductor It inthe manner of loom, or in a basket-weave arrangement. The casin Iisnugly engages the outer periphery of the conductor it and may have adiameter of several one-hundredths of an inch, thereby being of asizeable diameter in proportion to the diameter of said conductor andafiording adequate insulation therefor.

The material from which the casing ii is formed is important in that itmust have fair insulating properties insofar as electricity is con.-cerned, but must be capable of transmitting in an efllcient fashionconsiderable quantities of heat while retaining a high degree offlexibility. It is not necessary that the casing be an extremely goodinsulator as any losses that occur within it will add to the total heatoutput. Its principal requirement is that it be undamaged by heat andperform the nominal function of an insulator as indicated. Due to itsrelatively small diameter, the casing is adapted to undergo flexing andbending about a small radius without undue distortion or separation.Also, since an appreciable portion of the heat generated by this heatingelement arises from the conductor it, the casing ii must be capable oftransmitting this heat to the desired locality without being affected inany un-.

desirable fashion by such heat or by the high temperatures which may beattained.

Glass fiber has been found particularly advantageous for use in formingthe insulating casing II. The glass fiber may be formed into strands orcords and arranged about the conductor in in a basketweave much in thenature of electrical insulating loom. An insulating casing so formed isquite flexible and may undergo repeated bending and flexing withoutinjury. At the same time, the glass fiber offers a reasonable degree ofelectrical insulation while acting in an efiicient fashion to transmitheat generated in the conductor 10. Other materials, such as thehalogenated vinyl resins, are also suitable for forming this insulatingcasing.

In addition to its electrical insulating and heat transmitting function,the casing il contributes to a marked extent to the heat output of theheating element. As appears hereinafter, the casing separates twoconductors and has the nature of a dielectric. Hence, dielectric lossesoccur in said sleeve. The occurrence of these losses results in thegeneration of heat, and this heat is transmitted outwardly from thecasing.

The casing is enclosed within a continuous, tubular conductor l2 formedof metal or some other conducting material which may be similar ordissimilar to the material of the conductor Ill. The insulating casinghas a snug fit within the bore l3 of the tubular conductor I2 so as tospace the inner wall of said conductor radially outwardly a uniformdistance from the conductor l and to fill substantially the entire spacebetween the conductors in and I2. An outer insulating casing or sleeve Hhas a snug fit upon the outer periphery of the conductor l2, therebyenclosing the entire assembly and the composite conductor within aninsulating case. The outer insulator i4 is formed similarly to the innerinsulating casing ll, being illustrated in Fig. 1 as formed with abasketweave composed of individual strands or cords of glass fiberbrother suitable material such as certain of the temperature-resistantplastics.

In this manner, a unitary heating element is provided, said elementincluding a central conductor surrounded by, or disposed concentricallyof, a tubular conductor, said conductors being spaced one from the otherby an insulating casing and completely encased in an outer insulatingsleeve or casing which encloses the entire assembly. Although Fig. 1illustrates this heat-1118 element in a greatly magnified or enlargedfashion, it is to be kept in mind that the outside diameter of thecomplete element is relatively small, possiblyin the neighborhood of 1*;of an inch, so that a high degree or flexibility is retained by theelement. Due to the small crosssectional area, of the conductors ill andii, the same will possess a marked degree of resistancev to anelectrical current flowing therethrough. For this reason, several yardsof this heating element will possess a quite considerable degree ofresistance, and when incorporated into an electrical blanket orheating-pad, will be capable of dissipating sumcient electrical energyin the form of heat as to provide an eflicient and desirable heatingstructure. As before pointed out, an appreciable portion of this heatingis accomplished by means of the inner conductor it which preterably isthe smaller in cross-sectional area and oflers the greater resistance.This purely resistance heat of the inner conductor will be supplementedby the purely resistance heat contributed by the outer conductor i2. Tothis will be added the heat arising from the dielectric loss occur--vring within the confines of the inner insulator sleeve II. The totalheat output thus achieved reaches quite sizeable proportions in relationto the length of the element involved and its diameter. Ii the heatingelement is supplied with a high frequency alternating current, theapparent resistance of the conductors are increased due to skin effect.

In practice, the heating element is arranged in any desiredconfiguration within the area or surface to be heated, and one of twoalternative connecting arrangements employed. It the heating element isof sufilcient length and the frequency of the electric supply is highenough, it may not be necessary to connect electrically the outer endsof the conductors i0 and i2 since the entire quantity of electricalenergy put into said conductors may be dissipated with the entireelement acting as an open clrcuited transmission line having highlosses. However, for shorter lengths of the heating element it may bedesirable to connect the outer ends of the two conductors by fusing thetwo together within the outer conductor sleeve H. The two conductors,when so connected, represent a continuous resistance element extendingfrom one end of the heating element to the other, and return. Witheither arrangement, the two terminals or poles of the electrical systemwhich supplies electrical energy .to the heating element, may both beconnected gle point at which they may be connected to said source ofelectrical energy.

Obviously, many additional advantages result from this structure. Oneimportant advantage is the substantial elimination of the danger of openarcs or sparks resulting from a breaking or short-circuting of thiselement. If, for any reason, the insulating sleeve II should berupturedso as to permit arcing between the two conductors, such arcingwould be confined within the outer insulator sleeve ll so that therewould be no open are or flash which might result in burns orconfiagration. This advantage is to be contrasted with the situationthat obtains when using an ordinary resistance-type element. Suchelements are normally encased by a single layer of insulation, and whensuch insulation is separated for any reason, the conductor normally arcsto any other part of the circuit with which it comes in contact, which,in many cases, includes any grounded metallic object, thereby resultingin an open flash or arc with the obvious consequent danger.

Another advantage which flows from this structure is the protection ofpersons adjacent to the heating element from shock by the electricalcurrent flowing therethrough. Manifestly, to cause an electrical currentto flow, the conductors I0 and I: must be at different electricalpotentials. However, this difference of electrical potential is confinedwithin the outer insulator l4 thereby 'minimizing the possibility of aperson's being shocked by coming in contact with the two conductors. Byconnecting the outer conductor I! to the ground side of the source ofelectrical energy supplying this heating element and connecting theinner conductor ID to the "live or hot side of this source, thepossibility of a person's being shocked may be further minimized ordecreased.

In this connection, it is to be noted that the major portion of thepotential drop across the heating element occurs in the inner conductorl0, and that the potential gradient along the outer conductor I2 isrelatively low. This means that a person coming in contact with twoexposed portions of the outer conductor is less likely to be shocked andis subjected to such small voltage differences that harm is unlikely.The larger voltage differentials are confined to the inner conductor Illwhich is doubly shielded and insulated.

Still another advantage of this structure is that, when supplied withhigh frequency alternating current, so called standing waves occur whichcause the heating to be distributed unevenly throughout the length ofthe heater. This uneven distribution of heat may be utilized toconcentrate the heat at desired places. If on the other hand, uniformheatingis desired throughout the structure, a proper termination may bedesigned at the distant end which will permit this.

A valuable electrical heating system is provided when the describedheating element is supplied with a high frequency electrical current. Inthis system, the dielectric loss between the concentric conductors andthrough the insulator I I becomes of considerable magnitude and resultsin the generation of a large proportion of the total heat output. Innormal concentric or coaxial cables, the effort is to prevent orminimize such heat losses and dissipation of energy. In the presentsystem however, this heat loss may be eflectively employed by selectingfor the insulator I I a material having only fair electrical insulatingproperties but having good or excellent resistance to high temperaturesand good heat transfer characteristics. It is also desirable that thematerial have a high dielectric loss, that is, the property of polyvinylchloride.

converting the electrical energy of current passing therethrough intoheat energy. The sensible heat thus provided is rapidly passed from theeleinent by reason of its high heat transmissive naure.

Glass fiber is an insulating material having these desired properties,as are the halogenated vinyl resins. Thus when these materials are usedin the fabricating of the heating element set out herein, a structure isprovided which implements the heating system forming a part of thepresent invention. Whereas, in the past, an effort has been made toeliminate dielectric loss through the conductor, this loss is nowcapitalized upon and used as a means for conversion of electrical energyinto sensible heat energy. This is made possible by increasing thefrequency of alternation of the electrical current, resulting in anincrease in the heat created by dielectric loss. The

applicable range of frequencies appear, at the present, to be limited ona practical basis to the band from kilocycles to 40 megacycles, it beingobserved that within this range the dielectric loss becomes appreciableand may be employed as a means of heat generation. The upper limit ofthe band is set by the presently-existing practical boundaries uponsources of electrical power, but, on a theoretical basis, there is noupper limit for the range of frequencies which may be used. Below 100kilocycles, the dielectric loss effect is of minor importance andthemajor portion of the heating is accomplished by ordinary resistancemeans.

In Fig. 2 of the drawing is illustrated a modiflcation of thisinvention. In this modification, the same conductors I0 and I! areemployed, but the insulating casing and sleeve, II and H, are replacedby different types of sleeves, i5 and I respectively. The sleeves l5 andii are similar to one another and differ from the sleeves H and II inthat the insulating material is arranged in a serving or helical windingabout the outer periphery of th conductors in and II respectively. Thesame advantageous results are achieved by this structure and itrepresents merely a modification of form of the first example of theinvention described. If desired, the insulating sleeves may be formed ofdouble helices extending in opposite directions.

In Fig. 3 is shown an application of plastic insulation to this heatingelement. The insulation sleeves illustrated in Figs. 1 and 2 may beformed of any desirable or suitable type of plastic material, such asthe sllicones, polyethylene or In addition, such plastic material may beformed into an integral sleeve having an axial bore through which theconductor or conductors extend. Thus, in Fig. 3,, the central or innerconductor I0 passes through the central opening ll of a one-piece,moulded insulator sleeve I8. The insulating sleeve II in turn passesthrough the axial opening or bore I. of a tubular sleeve-like conductor20, and a tubular insulating sleeve or casing 2|, cast or extruded fromplastic material, has a snug fit over the outer periphery of theconductor 20. The insulators l8 and 2| function in the same fashion asthe insulators H and I4 and represent merely .a. modification of thelatter. As illustrated in Fig. 3, the outer, sleeve-like or tubularconductor 20 may b in th form of a metallic loom or shield having abasketweave similar to shielding employed in various radio andcommunication equipment. Indeed, the outer conductor may as- 76 sum:this form in the modifications shown in P188-1and2sinceallthatisnecessaryistonrovide a tubular conductor with respectto which the inner conductor can be concentrically disposed.

All of the forms achieve the same beneficial results, and being verysmall in diameter may be subjected to extensive and repeated flexing andbending. In particular, in the case of an electrically-heated blanket,this heating element may be incorporated into the weave of the blanketin place of certain of the threads thereof. In this fashion, an integralor built-in heating element may be provided in the blanket which isnotsubiect to misplacement or malfunctioning.

' The utilization of the heating element in a blanket is shown in Figs.7 through 10. In Fig. 7, a blanket 22 has the heating element 23disposed therein in a modified spiral outline. The inner and outerconductors of the heating element, it and it, are coupled through aninductive linkage 24 with a suitable oscillator 25 which supplieselectrical energy at high frequency. In this high frequency application,the remote end 28 (Fig. 9) of the heating element may or may not includea shorting together of the heating element conas ductors. in F18. 8.

An alternative and less expensive application of the heating element isshown in Fig. 10. In some ways, this form is preferred because of itssimplicity and direct use of commercial 60 cycle electric current. Thisapplication connects the conductors m and I2 of the heating elementdirectly to the power supply, and employs the shorted remote end 26shown in Fig. 9. As pointed out hercinbefore, the major portion of thevoltage drop across the heating element occurs in the inner conductorit) which is completely shielded and doubly insulated. The outerconductor, which a person is much more likely to come in contact with,has a very low potential gradient because of its larger size, and it istherefore improbable that a serious electrical shock could be receivedtherefrom.

The foregoing description of the invention is explanatory thereof andvarious changes in the size, shape and materials, as well as in thedetails of the illustrated construction may be made, within the scope ofthe appended claims, without departing from the spirit of the invention.

What I claim, and desire to secure by Letters Patent is:

1. An electric heating element comprising an elongate inner conductorsurrounded with electrical insulating material; an outer elongatedcylindrical conductor closely surrounding said insulating material, saidinner and outer conductors having means to electrically connect at oneend of the element in series with a pair of terminals of a source ofelectrical energy, said inner and outer conductors at the other end ofthe element being electrically connected together, said inner conductorhaving substantially higher electrical resistance than said outerconductor whereby substantially all of the potential drop of the heatingelement is confined to said inner conductor.

The details of the coupling are shown 2. An electric heating elementcomprising an 70 said insulating material, said inner and outer elongateinner conductor surrounded with electrical insulating material, saidinsulating material being characterized by high heat resistance highrate of heat transfer and high dielectric loss, an outer elongatedcylindrical conductor closely surrounding said insulating material. saidinner and outer conductors havins means to electrically connect atoneend of the element in series with a pair of terminals 01 a sourceoielectrical energy. said inner and outer conductors at s the other end ofthe element being electrically 10 fined to said inner conductor.

3. An electric heating element comprising an elongate inner conductorsurrounded with electrical insulating material, said insulating materialbeing characterized by high heat resistance 15 high rate of heattransfer and high dielectric loss, an outer elongated cylindricalconductor closely surrounding said insulating material. said inner andouter conductors having means to electrically connect at one end of theelement in W series with a pair of terminals of a source of alternatingcurrent, said inner and outer conductors at the other end of the elementbeing electrically connected together, said inner con.- ductor havingsubstantially higher electrical resistance than said outer conductorwhereby substantially all of the potential drop of the heating -elementis confined to said inner conductor.

l. An electric heating element comprising an elongate inner conductorsurrounded with electrical insulating material, an outer elongatedcylindrical conductor formed of similar conductive material to saidinner conductor and closely surrounding said insulating material, saidinner and outer conductors having means to electrically connect at oneend of the element in series with a pair of terminals oi a source ofelectrical energy, said inner and outer conductors at the other end ofthe element being electrically connected together, the cross-sectionaldimensions of said inner conductor being substantially less than thecross-sectional dimensions of said outer conductor to increase theresistance of said inner conductor relative to said outer conductorwhereby 35 substantially all of the potential drop of the heatingelement is confined to said inner conductor.

5. An electric heating element comprising an elongate inner conductorsurrounded with electrical insulating material, an outer elongatedcylindrical conductor formed of similar conductive material to saidinner conductor and closely surrounding said insulating material, saidinner and outer conductors having means to electrically connect at oneend of the element in series with a pair of terminals of a source ofaltematlng current, said inner and outer conductors at the' other end ofthe element being electrically connected together, the cross-sectionaldimensions of said inner conductor being substantially less than thecross-sectional dimensions of said outer conductor to increase theresistance of said inner conductor relative to said outer conductorwhereby substantially all of the potential drop of the heating element iconfined to said inner conduc- 6. An electric heating element comprisingan elongate inner copper conductor surrounded with electrical insulatingmaterial, an outer elongated cylindrical copper conductor closelysurrounding conductors having means to electrically connect at one endof the element in series with a pair of terminals of a source ofelectrical energy said inner and outer conductors at the other end of 76the element being electricall connected together.

9 i the cross-sectional dimensions of said inner con- REFERENCES CITEDductor being substantially less than the cross- The following referencesare of record in the sectional dimensions of said outer conductor to mof this patent: increase the resistance of said inner conductor relativeto said outer conductor whereby substan- 5 UNITED STATES PATENTS Itially all of the potential dropof the heating ele- Number Name Datement is confined to said inner conduct 4 1,432,064 Hadaway Oct. 17, 19222,387,829 Burnham et a1. Oct. 30, 1945 ANSEL CHALLENNER- 2,436,421 CorkFe 4,1

